Explaining the hows and whys of the Gould Hall HVAC System

1
Explaining the hows and whys of the Gould Hall
HVAC System

• How does the system operate and why has it been
  organized to operate in this manner?

2
The two tasks for an HVAC system providing
fresh air and maintaining occupant thermal
comfort

• Fresh air
• Clean and adequately spread throughout the
  building
• Thermal comfort determinants
• -- Environmental air temperature, relative
  humidity, air velocity (around an occupant), and
  radiant exchange rate (between occupant and
  his/her surroundings)
• -- Personal insulation value of occupants
  clothing ensemble and occupants activity rate

3
Figure A.6 The major spaces for the Gould Hall
mechanical (HVAC) system are presented here. The
mechanical room is located in a two-story high
space with its flooring set at the sub-basement
level. There are four shaft, each located in one
of the corners of the building. Off of these
shafts numbers of horizontal branch ducts run in
ceiling plenums (note that two sets of these
horizontal branches are shown in this
illustration.)
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So, what spaces are used for the Gould Hall HVAC
system?

• 1. Mechanical room
• Central air (supply) handler 3 used air fans
  steam convertor hot water pumps pipes ducts
• 2. Vertical shafts (4, one for each floor area
  quadrant)
• Supply air ducts return air passage (in shaft)
  HVAC piping
• 3. Ceiling plenums (between finished ceiling
  assembly and floor structure above)
• Horizontal ducting reheat terminals diffusers
  RA grilles ceiling plenums (as one type of
  volume for transporting RA to shafts)

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Gould Hall HVAC System

• Identified as an all-air system with
  supplemental radiation
• Air is supplied to spaces for VENTILATION
• Air is supplied to spaces for TEMPERATURE control
• Water is used for secondary heat supply
• For modifying temperatures of air streams
  entering building spaces
• As supplemental radiation

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For all-air systems (such as the Gould Hall HVAC
system)

• Fundamental differentiation between system types
• Constant volume of air supplied with the air
  temperature varied as needed, space-by-space
  VS. Air supplied at a constant temperature with
  the amount of air supplied varied as needed,
  space-by-space
• Designated as CAV vs. VAV

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Why is a CAV, VAT system good for Gould Hall?

• Consider the types and ranges of activities
  pursued in Gould
• Classrooms some small, others larger AND some
  only partially occupied, others full
• One and two-person offices
• Wood metals shop photo lab

8
As a digression, think about heat generation and
temperature regulation

• Heat loss occurs at building envelope
• Heat gain also occurs at bldg envelope solar
  gain ToagtTia
• Heat is generated inside buildings by people,
  electric lights, electric equipment
• ISSUE for system design operation which
  condition predominates (or which conditions
  predominate)?
• If heat gain rate gt heat loss rate, then air
  temperature will rise (if excess heat is not
  removed)

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Generic thermal behaviors for buildings

• 1. For internal spaces, heat generated by
  people, lamping, equipment will cause
  internal-load-dominance
• 2. For perimeter spaces where heat generated by
  PLE is small, then behavior will be determined by
  heat loss or heat gain rate at the envelope
• -- when heat loss or gain at envelope
  predominates, condition is described as
  envelope-load-dependent
• 3. In perimeter spaces where heat generated by
  PLE is larger than heat loss or gain rate at
  envelope, internal-load-dominance also prevails

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For Gould Hall system operation

• Some spaces classrooms, mostly are ILD when
  occupied
• Offices located mostly along E, N, W elevations
  are ELD
• ILD spaces require COOLING
• ELD spaces need HEATING (when Tia gt Toa)
• As both heating cooling are needed for various
  spaces in Gould at the same time, the HVAC system
  must have a VARIABLE AIR TEMPERATURE capability

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• Figure A.19 A summary of the Gould Hall
  air-handling system is presented here. The
  circling blackened arrows represent the supply
  and return air flows from the air handler to a
  classroom on an upper floor to the return air
  fan. The arrow to the right portrays the return
  air that is dumped to the building exterior after
  the air has been used. The arrow at the right
  front indicates the entrance of fresh air coming
  in from of the building. At the lower left is
  the steam-hot water convertor. Hot water in
  pipes flow from this convertor through pumps to
  the supply air handler, to reheat terminals, and
  to supplementary radiation. This drawing has
  been created as an alternative to the traditional
  one-line schematic system drawing that often is
  used to introduce the contents of a mechanical
  (HVAC) system in a construction documents set.

12

• Figure A.12 A prototypical steam-hot water
  convertor is shown. The steam enters at top back
  orifice and exits at the bottom. System water
  enters at the right end, flows through the bundle
  of tubes, and exits at the left end. The steam
  passes around the bundle of tubes transferring
  its heat through the walls of the tubes to the
  water. In the Gould Hall steam convertor --
  shown in Figure A.11 -- the water leaves at a
  temperature of about 140 ºF (60 C) and passes
  into the heating components of the overall
  mechanical (HVAC) system. The system through
  which the hot water passes is essentially a
  closed loop (with minimal water losses during
  circulation.)

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Figure A.13 These several pumps are used for
propelling hot water throughout the air-handling
and heating systems. The hot water comes from
the steam convertor that is along the wall just
to the right of the door. Note the pipes that
run from these pumps carrying the hot water to a
variety of systems components, both in the
mechanical room and elsewhere in the building.
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Figure A.23 A reflected ceiling plan shows two
reheat terminals. One of these terminals
conditions and ventilates the room in which these
terminals are. The other terminal services the
adjoining room. The circle within the enclosed
space one of the four shafts for this building
-- adjacent to the room is the vertical supply
air ducting for approximately one-quarter of the
building. The square in this enclosed space
represents the hole in the ceiling of the shaft
that allows return air to flow downward to the
return air fan that is located in the mechanical
room.
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• Figure A.24 One of the reheat terminals shown
  in Figure A.23 is visible here.

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For Gould Hall system operation (III)

• Temperature of air leaving Supply Air Handler is
  set to provide sufficient cooling for space with
  greatest ILD
• Air streams entering all other spaces will need
  to be heated to increase the temperatures of the
  streams for those spaces
• Note that the Outside Air is used as the cooling
  medium for the building
• Known as an economizer cycle of operation
• No reliance on chilled water supply from Power
  Plant

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Use of architectural radiation

• Large glazing areas in envelope present thermal
  comfort problems
• especially, because glazing is single-paned!
• Thermal comfort problems (caused by large
  windows)
• radiational exchange between occupants inside
  window surfaces
• convective drafts puddling across floors
• Solution provide supplemental radiation
  underneath window everywhere in Gould Hall

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Figure 2.7 The finned-tube "architectural
radiation" is composed of one or more metal tubes
through which hot water flows. Each tube has a
series of metal fins connected to the tube. When
the hot water flows through the tube, the thermal
energy from the hot water is conducted into the
wall of the tube and then out to the fins. The
warmed fins thus provide greatly-increased
surface areas for the promotion of convective
heat transfer to the air. The warmed air is
useful in heating any window glass surface that
is located just above this "architectural
radiation" device. (Radiant heat transfer also
occurs -- from the fins to the cabinet and then
from the cabinet to window surface -- but this
radiant transfer is less useful in warming the
cool glass surface).
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• Figure A.14 Supplemental radiation (or, as it is
  often called, architectural radiation) is
  placed underneath windows. Its function is to
  warm the window surfaces, thereby reducing the
  potential for room occupants to experience
  thermal discomfort resulting from otherwise
  too-cold window surfaces.